Solar flare effects on neutral gas glow in interplanetary space

Abstract

Solar flares in hydrogen and helium resonance lines (1216 and 584 Å) must be expected to result in temporal variations of neutral gas glow inside the heliosphere. Simultaneous measurements of glow variation and solar emission bursts proposed in this work would provide principally new experimental opportunities to derive the neutral atom number density distribution along the line-of-sight. Such a remote probing technique, similar in idea to radar, may be of great importance for the study of local interstellar medium-solar system interaction. The magnitude and occurrence frequency of solar flares in e.u.v. were assessed on the basis of the relation between e.u.v. flare emission enhancement and apparent solar flare area in Hα, for which data of solar patrol are available. The analytical expressions for glow temporal variations were obtained for a few model number density distributions similar to those expected for interstellar hydrogen and helium inside the heliosphere. The discussion of relevant instrumentation shows that a space experiment, based on the exploitation of the solar flare effect, seems to be marginally feasible for hydrogen atoms and could be successful for helium atoms.